1. Field of Invention
This invention pertains to an artificial heart device which is implanted within the chest cavity and is powered by a pneumatic pump. More particularly, it relates to a total artificial heart which is of semi-rigid shell construction with an internal compartment divided into a blood flow chamber and a pumping chamber by means of a flexible diaphragm.
2. Prior Art
The successful extension of life utilizing the Jarvik-7 (TM) total artificial heart (TAH) offered new options for patients awaiting heart transplants. In particular, terminal patients who might have had little hope for survival because of heart transplant shortages could now hope for extended life based on the use of an artificial heart implanted within the chest cavity and powered by an external pneumatic drive system.
The Jarvik-7 TAH is characteristic of prior art devices of this type. The Jarvik-7 was fabricated from either Avcothane-51 ELASTOMER (TM) or BIOMER (TM). The basic design and construction of this artificial heart has been well documented. See for example, "The Total Artificial Heart" by R. K. Jarvik, Scientific American 244:66 (1981). This TAH introduced the seamless blood contacting surface for ventricles, with a multi-layered diaphragm including (i) a blood contacting diaphragm as part of the ventricle wall, and (ii) multiple pumping diaphragm structures which respond to the inflation and deflation forces of the pneumatic drive system.
A major problem of the prior art TAH structure is the difficulty of fitting the shell and attached valving and tubing within the small space typically occupied by a natural heart. The large size of the TAH made implantation particularly difficult for the surgeon who was required to perform difficult suturing of connector valves at various attachment points of the circulatory system. Failure to achieve properly sutured junctions could encourage fatal thrombogenesis.
The geometric configuration of the Jarvik-7 was a circular structure whose minimum radius and depth were limited by the need for maintaining a desired stroke volume of 100 cc. This stroke volume represents the quantity of blood which can be displaced through the TAH with full displacement of the diaphragm as part of a pumping cycle.
For the Jarvik-7, a 100 cc stroke volume was realized for left and right ventricle devices having dimensions as shown in the following table.
TABLE 1 ______________________________________ LEFT RIGHT ______________________________________ Height 3.555" 3.435" Width 3.400" 3.350" Length 3.450" 4.010" Diaphragm Height 1.050" 1.050" ______________________________________
Because of the size limitation and space requirement for the Jarvik-7, implantation of such a TAH in patients less than 200 pounds was unrealistic. What was needed, therefore, was a TAH which was smaller in geometric configuration to allow implantation in smaller individuals, but which would maintain a sufficient stroke volume to meet patient needs.